1. Field of the Invention
The present invention pertains to novel compounds having a terminal alkoxypropenyl group, their manufacture, liquid crystalline mixtures which contain these compounds and their use for electro-optical purposes.
2. Description
Liquid crystals are used primarily as dielectrics in indicating devices, since the optical properties of such substances can be influenced by an applied voltage. Such indicating devices are well-known to a person skilled in the art and are, for example, cells having dynamic scattering, DAP cells (deformation of aligned phases), guest/host cells, TN cells having a twisted nematic structure, STN cells ("super twisted nematic"), SBE cells ("super birefringence effect") and OMI cells ("optical mode interference"). The most common indicating devices are based on the Schadt-Helfrich effect and have a twisted nematic structure.
Liquid crystal materials should have a good chemical and thermal stability and, moreover, should be stable to electric fields and electromagnetic radiation. At the usual operating temperatures they should have a suitable mesophase, for example a nematic, cholesteric or tilted smectic phase. Further, the liquid crystal materials should have a low viscosity and in the cells should give short response times, low threshold potentials and a high contrast.
Further properties such as the electrical conductivity, the dielectric anisotropy and the optical anisotropy must fulfil different requirements depending on the type of cell and field of application. For example, for cells having a twisted nematic structure, liquid crystal materials should have a positive dielectric anisotropy and an electrical conductivity which is as low as possible. In addition to the general interest in liquid crystal materials as possible. In addition to the general interest in liquid crystal materials having a high optical anisotropy, there has recently been an increased interest in materials having low optical anisotropy, especially for actively-addressed liquid crystal indicators, e.g. in the case of TFT applications ("thin film transistor") in television sets.
In order to optimize the properties of liquid crystals in the cell, liquid crystals are generally used as mixtures of several components. It is therefore important that the components have a good miscibility with one another. Cholesteric mixtures can preferably consist of one or more optically active dopants and a nematic liquid crystal material.